Transcript Electron Transport and ATP Synthesis

Electron Transport and ATP
Synthesis
C483 Spring 2013
1. To reduce one molecule of O2, ________ electron(s) must be passed through the
electron transport chain and ________ molecule(s) of NADH is(are) oxidized.
A) 4; 2
B) 2; 1
C) 1; 1
D) 1; 2
E) 4; 4
2. The chemiosmotic theory is a concept that ________.
A) the transport of Na+ and K+ across cell membranes is by active transport
B) explains how transport by facilitated diffusion reaches a saturation limit
C) explains the blood-brain barrier
D) a proton gradient drives the formation of ATP
3. Which is the proper ranking of greatest to least reduction potential?
A) NAD+, Q, O2
B) O2, Q, NAD+
C) Q, NAD+, O2
D) Q, O2, NAD+
4. According to the binding change mechanism, the (alpha3 beta3 ) oligomer of ATP
synthase has 3 catalytic sites which can each have ________ different conformations.
A) 2
B) 3
C) 6
D) 9
5. The P/O ratio for passing electrons through complexes I, III and IV is ________.
A) 1
B) 1.5
C) 2
D) 2.5
E) 3
Goal: ATP Synthesis
Overview
• Redox reactions
• Electron transport chain
• Proton gradient
• ATP synthesis
• Shuttles
Analogy: How does burning coal put flour in the grocery store?
Redox reactions: electricity
• 2 e- transfer
• Calculate DG by
reduction potential
• NADH: Eo’ = -.32
• FMN: Eo’=-.30
• DGo’ = -nFDEo’
= -2(96485)(0.02)
= -3.9 kJ/mol
Coenzyme Q: Mobile Carrier
• FADH2 is a one edonator
• Many reactions,
including metals
• Ubiquinone is a key
intermediate
• Can diffuse through
nonpolar regions easily
Numerous Redox Substrates
• O2: high “reduction potential”
• Substrates
– Organic cofactors
– Metals (iron/sulfur clusters)
– cytochromes
Oxygen: the final electron acceptor
• Water is produced—has very low reactivity, very
stable
• Superoxide, peroxide as toxic intermediates
• Overall reaction
NADH + H+ + ½ O2  NAD+ + H2O
Flow Through Complexes
Downhill Flow of Electrons
Compartmentalization
Protonmotive Force
• Flow of electrons is
useless if not
coupled to a useful
process
– Battery connected
to wire
• Proton gradient
across
mitochondrial
membrane
Overview of Complexes I-IV
• Don’t need to know which cofactors in which
complexes, mechanism of proton pumping
• Complex I and II are different entry points into
Q pool, which goes to Complex III
Protonmotive Force
• NADH + H+ + ½ O2  NAD+ + H2O + 10 H+ pumped
• succinate + ½ O2  fumarate + H2O + 6 H+ pumped
Proton Gradient
• Gradient driven by concentration difference +
charge difference
• Free energy of ATP hydrolysis = -48 kJ/mole
• How many protons needed to fuel ATP
formation? Minimum of 3
Using the Gradient
• Coupled to ATP synthesis
• Uncouplers used to show
link of oxygen uptake and
ATP synthesis
Complex V: ATP Synthase
• Molecular motor
• Rotor: c, g, e
– Proton channel
Proton Channel
• Protons enters channel
between rotor and stator
(unit a--purple)
• Rotor rotates to release
strain by allowing proton
to enter matrix
• “Stalk” (g) moves inside
the “knob”—hexameric
ATP synthase
• 9 or 10 protons = full
rotation
Binding-Change Mechanism
• Stalk causes ATP synthase to have three different
conformations: open, loose, tight
• In “tight” conformation, energy has been used to
cause an energy conformation that favors ATP
formation
• 9 protons = 3 ATP (or 1 ATP/3 protons)
Remember Analogy
• Fuelelectricitywater pumped
uphillflows down to grind flour
• But we don’t have bread until flour is
transported to where it needs to go!
• Compartmentalization: ATP is in matrix, but
must get to the rest of the cell
Active Transport of ATP
• ATP must go out, ADP and Pi must go in
• Together, use about 1 proton of protonmotive
force
Energy Accounting
• ATP costs 4 protons
– 3 protons in ATP synthase, 1 proton in transport
• NADH pumps 10 protons
– 4 protons in Complex I, 4 protons in Complex III, and
2 protons in Complex IV
– 2.5 ATP/NADH
• called P/O ratio--# of phosphorylation per oxygen atom
• QH2 pumps 6 protons
– 4 protons in Complex III and 2 protons in Complex IV
– 1.5 ATP/QH2
Net ATP Harvest from Glucose
• Glycolysis = 2 ATP
– Plus 3 or 5 ATP from
NADH
– What leads to
difference in this case?
• Pyruvate DH = 5 ATP
• Citric Acid Cycle = 20
ATP
• Total: 30-32
ATP/glucose
NADH Shuttles
• Glycerol phosphate
shuttle (1.5 ATP/NADH)
• Produces QH2
• Operational in some
tissues/circumstances
NADH Shuttles
• Malate-Aspartate
shuttle (2.5 ATP/NADH)
– Actually slightly less
because one proton is
consumed in shuttle
• Separate NAD+/NADH
pools indirectly
interconverted
• Operational in some
tissues/circumstances
Answers
1.
2.
3.
4.
5.
A
D
B
B
D